An electric arc furnace is an electrically operated furnace used for melting metal and/or for cleaning slag. The operation of the furnace is based on an arc flame that burns either between separate electrodes, or between electrodes and the material to be melted. The furnace may be operated either by AC or DC current. Heat is created in the arc flame, and also in the material to be melted, in case the arc flame burns between the material and the electrodes. Power is conducted to vertical electrodes that are located symmetrically in a triangle with respect to the midpoint of the furnace. In the case of a DC smelting furnace there is one electrode in the middle of the furnace. The assembly depth of the electrodes in the furnace is continuously adjusted, because they are worn at the tips owing to the arc flame.
The lower part of the electrode column assembly comprises a contact shoe ring, a pressure ring and a heat shield. The contact shoe ring consists of a plurality of contact shoe elements arranged as a ring to be in contact with a steel mantle inside of which the electrode paste is sintered. Such an electrode is a so-called Soderberg electrode. The contact shoe elements conduct electric current to the electrode. A pressure ring is arranged on the outside of the contact shoe ring, so that the contact shoe ring is surrounded by said pressure ring. The pressure ring consists of a plurality of pressure blocks connected with each other as a ring, which pressure blocks being provided with hydraulic bellows by which the contact shoes in the contact shoe ring are pressed against the steel mantle of the electrode. A heat shield surrounding the electrode column assembly is arranged above the pressure ring in the axial direction of the electrode column assembly. Also the heat shield is comprised of a plurality of segments connected with each other to form an assembly of annular form.
As mentioned above, the pressure ring consists of a plurality of pressure blocks connected with each other as a ring. The pressure blocks are commonly made of massive copper elements. In current systems the connections between the pressure blocks are quite often manufactured so that shoulders or ridges are machined in the side edges of the copper elements. So, in this kind of arrangement, in the manufacturing stage, extra copper material must be reserved of the copper cast molding, half of which extra material must be cut away to obtain a shoulder. Therefore material is wasted.
Through holes for bolts or screws are made in the above mentioned shoulders and the adjacent pressure blocks are connected to each other by said bolts or screws. This causes a disadvantage or drawback because the high tensile stress prevailing in the pressure ring is directed to the shearing stress of the bolts. Therefore it is very likely that in use cleavage will occur in the seams between adjacent pressure blocks.
Another drawback will become obvious when a single contact shoe must be changed. Due to the shoulders three pressure blocks must be detached to change a single contact shoe.
With further reference to prior art document EP1971190 shows a pressure ring assembly in which adjacent pressure blocks are connected to each other with a separate connecting means. For said connecting means grooves are machined on the side edges of the pressure blocks and the connecting means is pushed in said grooves from above. The connecting means has a tapering form in the longitudinal direction of it and therefore it is very difficult to detach the connecting means after it has been mounted in place.